1. Technical Field
The present invention relates to the use of bandwidth in a Synchronous Optical Network (SONET) ring. More particularly, the present invention is a method, for use in transmitting broadcast traffic (point to multi-point), of trading protection bandwidth in a uni-directional path-switched (UPS) SONET ring for un-protected usable bandwidth.
2. Description of Related Art
SONET is the ANSI standard for advanced fiber optic transmission. Under SONET, network elements can communicate in a ring by passing information frames. In these rings entire communication streams are collected and routed within a level one or higher synchronous transport signal (STS-1 or higher) frame, instead of being de-multiplexed and multiplexed each time a signal is added or dropped. Besides STS-1 signals, multiples of these communications signals may be synchronously multiplexed into higher rate STS-N signals. STS-N signals are then converted to optical OC-N signals for transport through fiber optic media.
FIG. 1 (prior art) is a simplified block diagram illustrating various definitions of the transmission network that interconnect different kinds of SONET network elements. Specifically, the SONET line, section, and path definitions are illustrated. FIG. 1 further illustrates path terminating equipment 10a-b, line terminating equipment 11a-b, and section terminating equipment 12a-b. A network element is said to be xe2x80x9cterminatingxe2x80x9d if during normal operation it may alter the information associated with the network section it terminates. For example, path terminating equipment 10a-b is defined to be equipment which is permitted to alter the path portion of a SONET frame; and an example of STS-1 path terminating equipment is an add/drop multiplexer. (An add/drop multiplexer is also line and section terminating equipment, because a device specified as capable of terminating one category of information necessarily can terminate subset categories.)
FIG. 2 is a schematic representation of a prior art UPS SONET ring 30, i.e., a SONET ring network in which a traffic stream 36 is split into two copies at network element 31 so that one copy travels in one direction in one medium 35a between network elements 31-34 along the ring, while a redundant copy is propagated in the opposite direction in another medium 35b, the traffic stream 36 shown being removed from the network element 33. Both rings 35a and 35b of the UPS SONET ring network traverse various network elements 31-34 positioned along the ring network. FIG. 2 in particular illustrates a traffic stream being added to the ring at network element 31, and the traffic stream being dropped (removed) from the ring at network element 33.
Each network element comprises network terminating equipment. Examples of network terminating equipment include traffic splitters and ring selectors. A traffic splitter 31a is shown included as part of network element 31. A ring selector 33a is shown included as part of network element 33.
A UPS SONET ring network, by transmitting the same information in opposite directions on two separate paths, provides each network element redundant information and thereby protects the information. If greater bandwidth is needed in an application, four-fiber bi-directional rings and optical upgrades, such as from OC3 to OC12, can be used but are expensive. Moreover, in some applications such as video or data broadcasting, it is not necessary or cost-effective to protect information.
What is needed is a way of making use of the bandwidth of a UPS SONET ring reserved for redundant information in applications where that redundancy is not needed or is not cost-effective.
The present invention is a method, for use in broadcast transmissions (point to multi-point), that converts some or all of the bandwidth of a classically protected uni-directional path-switched SONET ring network path to a single-thread (non-redundant) path with up to twice the bandwidth of the classical SONET ring network. The invention does not necessarily eliminate or change the architecture of a network providing a redundant ring, but is rather an overlay that can coexist with such an architecture.
According to the present invention, at a network element that is a source for transmitting information onto a UPS SONET ring network, non-redundant traffic is transmitted into the network on only one of the redundant paths within the ring. At the receiving network elements, this non-protected traffic is bridged such that it is both dropped at the network element and transmitted to the next down-stream network element. This leaves the path in the opposite direction available to carry an equal amount of non-redundant traffic.
Thus, in a UPS SONET ring network altered according to the present invention, both paths of the network transmit non-redundant information, thereby doubling the Path bandwidth by sacrificing protection. If the invention is applied to all paths within the network, the network is essentially converted into an unprotected linear configuration. However, the great utility of the invention is that both traffic classes, protected and unprotected, can be carried in the same network at the same time without extensive changes to existing equipment.